The present invention relates to an ignition control method for an internal combustion engine such as an automotive engine, and more particularly, it relates to an ignition control method capable of preventing erroneous ignition control for improved safety.
In order for a multi-cylinder internal combustion engine to properly operate, ignition for each cylinder must take place as prescribed piston positions or rotational angles of the crankshaft of the engine, i.e., at the times when each piston of the engine is at a prescribed position with respect to top dead center. To this end, it is necessary to sense a predetermined reference crank angle or position for each cylinder and identify which cylinder is at the reference crank angle or position.
FIG. 3 illustrates, in a schematic block diagram, a known ignition control apparatus for an internal combustion engine. The apparatus illustrated includes the following elements which will be described below. A signal generator SG generates, in synchronism with the rotation of the engine, a reference signal SGT indicating predetermined crank angles or positions for each cylinder and a cylinder identification signal SGC containing square pulses for identifying the respective cylinders. The reference signal SGT contains a series of plural square pulses each of which has a leading or rising edge representative of a first reference crank position of a corresponding cylinder, and a trailing or falling edge representative of a second reference crank position thereof. An engine operation sensor (not shown) senses the operating condition of an engine such as the engine load, the speed of a vehicle on which the engine is installed, etc., and generates a corresponding engine operating condition signal D. A period measuring means 1 detects the first and second reference positions for each cylinder based on the reference signal SGT. A target ignition timing calculator 2 calculates, based on the engine operating condition signal D, a target ignition timing .theta. for each cylinder, at which ignition is to take place, as well as a power supply starting timing for each cylinder, at which the power supply to an ignition coil for a cylinder is started. A time calculating means 3 calculates, based on the target ignition timings, an angular distance in time from the first and second reference positions to the target ignition timings and the power supply starting timings for respective cylinders. A timer means 4 sets an ignition control time T for each cylinder based on the reference signal SGT and the angular distance in time calculated by the time calculating means 3. A cylinder identifying means 5 identifies, based on the reference signal SGT and the cylinder identification signal SGC, which cylinder is at the first or second reference position as detected. Based on the output signal of the timer means 4 and the output signal from the cylinder identification means 5, an electronic distributing means 6 controls the ignition timing of the individual identified cylinders in accordance with the ignition control time T. A plurality of power transistors 7 for controlling the conduction of corresponding ignition coils 8, each of which is provided for a corresponding cylinder, are turned on and off by the distributing means 6 in a prescribed sequence.
Though not illustrated in detail, the above-mentioned elements 1 through 6 are incorporated in an electronic control unit ECU (not shown) such as a microcomputer. In addition, each of the ignition coils 8 has a primary winding connected to a corresponding power transistor 7 and a secondary winding connected to a corresponding spark plug (not shown) having a spark gap.
FIG. 4 is a timing chart showing the relationship between the reference signal SGT and the cylinder identification signal SGC, in which B75.degree. indicates the first reference position, i.e., the rising edge of a pulse of the reference signal SGT which takes place at a crank angle of 75.degree. before top dead center (BTDC), and B5.degree. indicates the second reference position, i.e., the falling edge of a pulse of the reference signal SGT which takes place at a crank angle of 5.degree. BTDC.
Here, the reference signal SGT and the cylinder identification signal SGC as illustrated are for a four-cylinder internal combustion engine. Based on the voltage level of the cylinder identification signal SGC at the second reference position B5.degree. of a pulse of the reference signal SGT and at the first reference position B75.degree. of the following SGT pulse, the cylinder identifying means 5 sequentially identifies the cylinders #1, #3, #4 and #2 in this order, so the operations of the cylinders are controlled in the same order.
FIG. 5 is a timing chart showing the relationship between the reference signal SGT and the current flowing in the ignition coils in which Tr represents the period between successive ignition control points; Ts a time duration from the first reference position of B75.degree. to the power supply cut-off point (i.e., ignition point); Ton1 a time duration from the first reference position B75.degree. to the current power supply starting point for a second ignition coil 8 at which current I.sub.2 starts to be supplied to the second ignition coil 8 for cylinder #2; Ton2 a time duration from the preceding second reference position B5.degree. to the power supply starting point for the second ignition coil 8; and Ton3 a time duration from the preceding ignition or power supply cut-off point for a first ignition coil 8 for cylinder #1, to a current power supply starting point at which current I.sub.2 starts to be supplied to the second ignition coil 8. In this regard, it is to be noted that the ignition time Ts as well as the respective time durations Ton1, Ton2 and Ton3 are included in the ignition control time signal T supplied from the timer means 4 to the distributor 6.
The operation of the above-mentioned known ignition control apparatus will now be described in some detail with reference to FIGS. 3 through 5.
The signal generator SG generates, in synchronism with the rotation of the engine, a reference signal SGT containing a series of square pulses each of which rises at the first reference position B75.degree. (i.e., at 75.degree. BTDC) and falls at the second reference position B5.degree. (i.e., at 5.degree. BTDC), and a cylinder identification signal SGC. The reference signal SGT thus generated is input to the period measuring means 1 and the cylinder identifying means 5, whereas the cylinder identifying signal SGC is input to the cylinder identifying means 5.
The cylinder identifying means 5 identifies the respective cylinders based on the level of the cylinder identification signal SGC at the respective first and second reference position of each pulse contained in the reference signal SGT. For example, as shown in FIG. 4, on the basis of the level of the cylinder identification signal SGC at the second reference position B5.degree. of a preceding SGT pulse and at the first reference position B75.degree. of the current SGT pulse, the cylinder identifying means 5 identifies the cylinder corresponding to the current SGT pulse as follows. If the SGC signal levels at these successive two points are low and high (i.e., 0, 1), respectively, it is then determined that the current SGT pulse corresponds to a first cylinder #1; if they are high and low (i.e., 1, 0), the current SGT pulse corresponds to a third cylinder #3; if they are high and high (i.e., 1, 1), it corresponds to a fourth cylinder #4; and if they are low and low (i.e., 0, 0), it corresponds to a second cylinder #2.
On the other hand, the engine operation signal D from the unillustrated engine operation sensor is input to the target ignition timing calculating means 2 which calculates, based thereon, a target ignition timing .theta., which corresponds to a crank angle at which ignition is to take place, in accordance with the operating condition of the engine as sensed.
The time calculating means 3 calculates, based on the target ignition timing .theta. and the period signal from the period measuring means 1, an angular distance in time from the current first reference position to the target ignition timing .theta., and outputs it to the timer means 4 which generates, based on the angular distance and the reference signal SGT, an ignition control signal T to the distributing means 6.
Based on the ignition control signal T, the distributing means 6 triggers the power transistor 7 for the cylinder to be controlled to turn it on at a point in time at which a predetermined time Ton has elapsed from the predetermined reference position, thus starting the power supply to a corresponding ignition coil 8, and then turns it off at a time point at which a predetermined time Ts has elapsed from the reference position, thus cutting off the power supply to the ignition coil.
The cut-off of the power supply is sequentially effected in the order of cylinder #1, #3, #4 and #2. In addition, the target ignition point T varies depending on the engine operating condition. For example, in cases where current I.sub.2 supplied to the second ignition coil 8 for the second cylinder #2 is controlled, as shown in FIG. 5, the power supply starting point and the power supply cut-off point are both controlled in an ignition-retarding direction under a light or low engine load, so a time duration Ton1 counting from the first reference position B75.degree. is selected. On the other hand, under a heavy or high engine load, both the power supply starting point and the power supply cut-off point are controlled in an ignition-advancing direction, so a time duration Ton2 from the second reference position B5.degree. of a preceding SGT pulse for the preceding cylinder or a time duration Ton3 from the falling edge of the preceding ignition coil current I.sub.1 (i.e., the cut-off time of the power supply to the ignition coil for the preceding cylinder) is selected to enable the power supply to be controlled at a point in advance of the first reference position B75.degree. of the current cylinder being controlled.
In this manner, taking the first and second reference positions B75.degree., B5.degree. or the ignition point of a previously controlled cylinder as a reference point, a target ignition control point T including the power supply starting point Ton and the power supply cut-off point Ts is controlled so that the cylinders are ignited in a usual timer-controlled manner.
In this connection, the cylinder identification means 5 generally includes memory means for automatically coinciding, after first cylinder identification, successive reference signal pulses with the remaining cylinders.
In this case, however, once a reference signal pulse for a certain cylinder is misidentified, a series of reference signal pulses thereafter successively input to the cylinder identifying means 5 are all misidentified, so ignition control is effected based on the erroneous cylinder identification.